1. Field of the Invention
This invention relates to a gas filtration apparatus and process, and more particularly to a gas filtration apparatus and process which combines heating with sonic agglomeration and porous cross flow filtration for liquid droplet removal.
Gas streams comprising small solid particles and/or liquid droplets are produced by many chemical processes and by combustion processes, such as in the effluent gas stream of coal gasifiers. Such particulate matter, liquid droplets and frequently, undesired gases, should be removed before the gas stream is passed to downstream equipment or processes or is released to the atmosphere. It has been especially difficult to remove such particulate matter from high temperature and high pressure gas streams frequently encountered. Many of the conventional methods, such as cyclones and electrostatic precipitation, fail under high pressure and temperature conditions. Particles and droplets which are over 10 microns in diameter may be removed from gas streams by conventional porous filters and the like, but smaller particles and droplets are difficult to remove because the porosity of the filter must be so small that it creates a substantial pressure drop across the filter. This is undesirable because the higher pressure drop requires greater energy and may inhibit the combustion process. Thus, porous flow filters do not remove small particles or liquid droplets from gas streams efficiently. Liquid droplets may be more efficiently filtered by a cross flow filter than solid particles of corresponding size.
Small droplets in a turbulent gas stream collide with each other and may agglomerate with other droplets on impact to form larger agglomerates. The number of collisions may be increased by confining the stream in a tube or flue, and subjecting the droplets in the flue to a sonic field. Sonic agglomeration has been used for many years to agglomerate small solid particles or liquid droplets into larger agglomerates. Liquid droplets are easier to agglomerate by sonic agglomeration than solid particles of corresponding size.